1. Technical Field
The present invention relates to security systems and, more particularly, to systems for allowing an alarm message to be conveyed from a vehicle which is under threat of, for example, a hijack attack. The vehicle to be protected may be of any type such as a heavy goods vehicle carrying a commercial load of value, or a motor car carrying important passengers, cash or valuable goods. The system of the invention may also be modified to provide a portable security unit.
2. Prior Art
There are security systems available which incorporate anti-hijack features. In some proposed systems the driver is able to activate an audible warning, such as a siren or a horn and/or immobilize the vehicle. Since the operation of such a system is obvious to the attacker, it may cause a violent reaction and this may increase the danger to the driver and/or passengers. There also exist various automatic vehicle location systems which, by means of radio signals, allow a central station to monitor the position of a vehicle continuously. These systems can also incorporate a device which is intended to be operated by the driver when attacked in order to send a coded radio message to the central station. In this way the central station knows exactly where a vehicle under attack is located. Unfortunately such automatic vehicle location systems are extremely complex and expensive. Such technology is therefore not appropriate to small commercial vehicle users, particularly if they only own a small fleet.
It is now becoming increasingly common for vehicles to be fitted with radio transmitting devices. Such devices include cellular radio telephones, Citizen's Band (CB) radio, and Private Mobile Radio (PMR) sets. Because of the nature of a cellular telephone system, the location of any telephone to within a single cell can be identified by the network operator. However, a cell can be relatively large so that unless the driver of a vehicle under attack is able to give his precise location when making an emergency call, there is still a problem of locating the vehicle. Moreover, it is not possible to make a telephone call covertly so that using a cellular telephone may give rise to an increased danger of personal attack from the hijacker.
In PMR systems, all mobile radios in a fleet are connected to at least one common base station. Some available equipment includes a device for making an automatic emergency call to this base station. Although the base station will then be aware that a vehicle is under attack, it has no way of establishing the location of that vehicle unless the driver is able to speak to the base station to give his location. Once again, this may give rise to an increased risk of personal attack from the hijacker.
Another requirement for providing for the security of a vehicle load arises in relation to refrigerated vehicles. The breakdown of the refrigeration system in transit can incur considerable financial penalties to the vehicle operator. Such a breakdown may not be noted by the driver himself. It is also unlikely that he would be able to take any remedial action to repair the refrigeration system without outside assistance.